The present invention relates to a method for digital image interpolation and sharpness enhancement, and particularly relates to a pixel interpolation for enhancing the edge sharpness of a digital image.
Currently, digital image has been increasingly applied in various field of image display, since its features such as clearness, non-disturbance, and easy to process, digital image has received large amount of material resources and man power investment in the research and development from global manufacture and research institute. The applications of digital image in devices such as cathode ray tube (CRT), liquid crystal display (LCD), digital projector, and bulletin display have already gained noticeable achievement in the display and process of digital image data.
In the processing of pattern or digital image data, for example magnification and reduction of pattern or image, most manufactures usually adapts image interpolation to maintain the sharpness of processed image, however, such method always generates at the edge of magnified or reduced image a poor sharpness.
Defect of poor edge sharpness is significant especially in a liquid crystal display and color digital image with screen of large-scale (for example larger than 15xe2x80x3). As shown in FIG. 1, a block diagram showing a method for digital image interpolation in accordance with prior art, in which only a bi-cubic filter is adapted to perform a digital image interpolation. The degradation of sharpness is due to low-pass filters employed which produce a new pixel by proportionally summing up certain adjacent pixels and result in blur and distortion at the edge of image. That is, prior image interpolation method performs interpolation for all pixels of entire image, therefore defects such as distortion or degraded sharpness appear at the edge of image.
Therefore, an object of present invention is to provide a method for digital image interpolation and sharpness enhancement. With such method, it is possible to improve the sharpness of the digital image at the edge, to achieve a preferred adjustable sharpness level, and to maintain low frequency components in the pattern or image without changing the filtering coefficient of a filter.
To achieve above object, a method for digital image interpolation and sharpness enhancement is provided in accordance with the present invention, this method comprises the following steps:
1) inputting an image (or pattern) signal Xij to a first interpolation low pass filter FIR 1, said FIR 1 is a cubic interpolation filter having filter coefficient hi(n);
2) inputting an image signal Xij to at least one of second interpolation low pass filters FIR 2, said FIR 2 is an interpolation filter having filter coefficient hixe2x80x2(n), wherein said FIR 2 has a cut-off frequency lower than that of said FIR 1;
3) making FIR 1 outputted via a band pass filter to obtain an image signal tij;
4) making FIR 2 outputted via a delay buffer to obtain an image signal tijxe2x80x2;
5) inputting said image signal tij and tijxe2x80x2 to a subtractor to obtain a differential signal tijxe2x88x92tijxe2x80x2; and
6) obtaining an output of image (or pattern) signal Yij by means of the following equation:
Yij=tij+Sxc2x7(tijxe2x88x92tijxe2x80x2),
where S is a sharpness level control coefficient.